To greet someone in a gangster like fashion. But all social groups can use it. Kind of like what's up but way cooler.
Jerome: yo what's ill bruh
Anj: OMG he said what's ill he must be so cool.
Sam: what's ill girlies.
noun. mect
1. Military Excellence Competition Team
2. It's what you make of it
Mect is all about embracing the suck and is NOT a cult.